Cooling for torque converter-equipped automatic transmissions is typically provided by a transmission heat exchanger that transfers the transmission oil heat to the engine coolant. Accordingly, transmission oil temperature is affected by engine coolant temperature, the engine cooling system's volume, and the engine cooling system's ability to reduce the additional transmission heat load. Similarly, engine coolant temperature is affected by transmission oil temperature, the engine cooling system's volume, and the engine cooling system's ability to reduce the additional transmission heat load.
It may be desirable to reduce the transmission oil temperature and/or engine coolant temperature beyond that which is possible with a given vehicle's engine cooling system. As an example, several systems adapted to reduce emissions (i.e., recirculating exhaust gas to reduce oxides of nitrogen) generate additional heat. For such systems, it may be advantageous to maintain transmission oil temperature and/or engine coolant temperature below a predetermined limit without increasing the engine cooling system's capacity.